1. Field of the Invention
The present invention relates to an apparatus in which an electronic device is carried on a substrate, and the electronic device and the substrate are connected to each other by a wire.
2. Description of the Related Art
An example of an apparatus in which an electronic device is connected to a substrate by wire bonding is a surface acoustic wave resonator 100 shown in FIG. 8. The surface acoustic wave resonator 100 includes a surface acoustic wave device 110 as an electronic device, a substrate 120, and a metal cover 130.
In the surface acoustic wave device 110, a vibrating electrode pattern 111 and a device electrode pad 112 are formed on a piezoelectric substrate composed of quartz crystal, lithium niobate, or the like.
A cavity 121 carrying the surface acoustic wave device 110 is formed in the substrate 120, a step 123 having a connecting conductor pattern 122 formed therein is provided inside the cavity 121, and a seal ring 124 for sealing is attached to a portion surrounding an opening of the cavity 121. The connecting conductor pattern 122 is so constructed as to be electrically connected to a terminal electrode 125 formed on an outer surface of the substrate 120 through an internal wiring pattern, a via hole conductor, or the like formed in the substrate 120.
The device electrode pad 112 and the connecting conductor pattern 122 are connected to each other by a wire thin line 140. Although the wire thin line 140 is fixed to the device electrode pad 112 and the connecting conductor pattern 122 in bonding portions at both its ends, its arch-shaped wired portion is in a free state where there is no restraint inside the cavity 121.
The above-mentioned surface acoustic wave resonator 100 is frequently subjected to ultrasonic vibration when or after it is mounted on a mother board or the like of electronic equipment. For example, in processes such as a flux washing process after reflow soldering, ultrasonic resin welding for fixing a substrate or parts, and wire bonding further performed for connection from the mother board to an external circuit, ultrasonic vibration of 15 KHz to 60 KHz is generally used. Accordingly, the ultrasonic vibration is also applied to the surface acoustic wave resonator 100.
The above-mentioned surface acoustic wave resonator 100 may, in some cases, be used as an in-vehicle part. In this case, significantly strong vibration such as the vibration of the engine or the vibration at the time of traveling is applied over a long time period. Therefore, the surface acoustic wave resonator 100 is used under significantly severe conditions which cannot be compared with a normal household part.
When such vibrations are applied, the arch-shaped wired portion in a free state where there is no restraint of the wire thin line 140 vibrates in the above-mentioned conventional surface acoustic wave resonator 100. The vibration of the wire thin line 140 can be grasped as the vibration of a string whose both ends are fixed. At this time, when the frequency of the applied vibration and the characteristic frequency of the wire thin line 140 coincide with each other, the wire thin line 140 resonates with the applied vibration. As a result, the amplitude of vibration of the wire thin line 140 is significantly increased exponentially, and the vibration is continued.
Consequently, elastic fatigue occurs in the wire thin line 140, thereby causing the possibility that there occur situations where the wire thin line 140 is broken, so that its electrical connection is interrupted. Particularly in the case of the in-vehicle part, the breaking and the disconnection may lead to an extremely grave and fatal accident.
An advantage of the present invention is to provide an apparatus carrying an electronic device, in which high reliability can be ensured without a wire thin line being disconnected by being broken even if ultrasonic vibration at the time of or after mounting on a mother board or strong mechanical vibration of an in-vehicle mount or the like is applied for a long time period.